Issue 6446 - Ignore emulated selectors if unchanged

include.preload.js

 /*
  * This file is part of Adblock Plus <https://adblockplus.org/>,
  * Copyright (C) 2006-present eyeo GmbH
  *
  * Adblock Plus is free software: you can redistribute it and/or modify
  * it under the terms of the GNU General Public License version 3 as
  * published by the Free Software Foundation.
  *
  * Adblock Plus is distributed in the hope that it will be useful,
  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  * GNU General Public License for more details.
  *
  * You should have received a copy of the GNU General Public License
  * along with Adblock Plus.  If not, see <http://www.gnu.org/licenses/>.
  */
 
 "use strict";
 
 let {splitSelector} = require("common");
 let {ElemHideEmulation} = require("content_elemHideEmulation");
 
+const {hash} = require("hash");
+
 // This variable is also used by our other content scripts.
 let elemhide;
 
 const typeMap = new Map([
   ["img", "IMAGE"],
   ["input", "IMAGE"],
   ["picture", "IMAGE"],
   ["audio", "MEDIA"],
   ["video", "MEDIA"],
   ["frame", "SUBDOCUMENT"],
   ["iframe", "SUBDOCUMENT"],
   ["object", "OBJECT"],
   ["embed", "OBJECT"]
 ]);
 
+function hashSelectors(selectors)
+{
+  if (!selectors || selectors.length == 0)
+    return 0;
+  return hash(new TextEncoder("utf-8").encode(selectors.join()));
+}
+
 function getURLsFromObjectElement(element)
 {
   let url = element.getAttribute("data");
   if (url)
     return [url];
 
   for (let child of element.children)
   {
     if (child.localName != "param")
       continue;
@@ skipping 292 matching lines @@
 };
 
 function ElemHide()
 {
   this.shadow = this.createShadowTree();
   this.styles = new Map();
   this.tracer = null;
   this.inline = true;
   this.inlineEmulated = true;
   this.emulatedPatterns = null;
+  this.digests = new Map();
 
   this.elemHideEmulation = new ElemHideEmulation(
     this.addSelectors.bind(this),
     this.hideElements.bind(this)
   );
 }
 ElemHide.prototype = {
   selectorGroupSize: 1024,
 
+  selectorsChanged(selectors, groupName)
+  {
+    let digest = hashSelectors(selectors);
+    if (digest == this.digests.get(groupName))
+      return false;
+    this.digests.set(groupName, digest);
+    return true;
+  },
+
   createShadowTree()
   {
     // Use Shadow DOM if available as to not mess with with web pages that
     // rely on the order of their own <style> tags (#309). However, creating
     // a shadow root breaks running CSS transitions. So we have to create
     // the shadow root before transistions might start (#452).
     if (!("createShadowRoot" in document.documentElement))
       return null;
 
     // Using shadow DOM causes issues on some Google websites,
@@ skipping 78 matching lines @@
       let selector = preparedSelectors.slice(
         i, i + this.selectorGroupSize
       ).join(", ");
       style.sheet.insertRule(selector + "{display: none !important;}",
                              style.sheet.cssRules.length);
     }
   },
 
   addSelectors(selectors, filters)
   {
+    if (!this.selectorsChanged(selectors, "emulated"))

[Manish Jethani, 2018/03/07 16:03:22]

This will go well with the collapsing selectors:

https://codereview.adblockplus.org/29670575/

We can just keep a hash of the current selectors, then just update it. I think I
could update the hash function to do incremental hashing.

+      return;
+
     if (this.inline || this.inlineEmulated)
     {
       // Insert the style rules inline if we have been instructed by the
       // background page to do so. This is usually the case, except on platforms
       // that do support user stylesheets via the browser.tabs.insertCSS API
       // (Firefox 53 onwards for now and possibly Chrome in the near future).
       // Once all supported platforms have implemented this API, we can remove
       // the code below. See issue #5090.
       // Related Chrome and Firefox issues:
       // https://bugs.chromium.org/p/chromium/issues/detail?id=632009
@@ skipping 70 matching lines @@
     let element = event.target;
     if (/^i?frame$/.test(element.localName))
       checkCollapse(element);
   }, true);
 }
 
 window.checkCollapse = checkCollapse;
 window.elemhide = elemhide;
 window.typeMap = typeMap;
 window.getURLsFromElement = getURLsFromElement;